PHP รบกวนสอบถามเรื่อง Authentication ใน IIS เขียนโค้ดรับค่าและนำค่ามาทำการ logout ไม่ได้

if (!isset($_SERVER['PHP_AUTH_USER'])) {
header('WWW-Authenticate: Basic realm="My Realm"');
header('HTTP/1.0 401 Unauthorized');
echo '....Text to send if user hits Cancel button ....';
exit;
} else {
	$sqluser = "SELECT * , SUBSTRING(level2,1,1) as newlevel2 FROM MSCMain.dbo.Employee Where user_login = REPLACE('$_SERVER[PHP_AUTH_USER]','metrosystems\','') and employee_status = '1' and user_login <> ''";
			echo $sqluser;
			$sql_user = odbc_exec($connid,$sqluser);
			if (odbc_num_rows($sql_user) != 0) { 
				$arrayuser = odbc_fetch_array($sql_user);
				$userLogin = $arrayuser['user_login'];
				$comp = $arrayuser['company_code'];
				$level2 = $arrayuser['level2'];
				$level1 = $arrayuser['level1'];
				$levelStr = $arrayuser['newlevel2']; 
				$_SESSION["username"] = $_SERVER['PHP_AUTH_USER'];
				$_SESSION["password"] = $_SERVER['PHP_AUTH_PW'];
				echo "User name :> {$_SERVER['PHP_AUTH_USER']}<br>";
				echo "Password :> {$_SERVER['PHP_AUTH_PW']} <hr>";
				echo "<a href='?action=logOut'>Logout</a>";
			}
			else{
				header('WWW-Authenticate: Basic realm="My Realm"');
				header('HTTP/1.0 401 Unauthorized');
				echo "You can't login / login agin plase.";
				exit;	
			}
}

session_destroy();
    if (isset($_SESSION['username'])) {
		echo ($_SESSION['username']);
        session_unset($_SESSION['username']);
        echo "You've successfully logged out<br>";
        echo '<p><a href="?action=logIn">LogIn</a></p>';
    } else {
        header("Location: ?action=logIn", TRUE, 301);
    };